Field of the Invention
The present invention relates to a lens apparatus having a image stabilization function, and more particularly, to a lens apparatus having a zooming function for a video camera, a silver-halide camera, a digital still camera, and the like, and to an image pickup apparatus including the lens apparatus.
Description of the Related Art
Heretofore, an image pickup apparatus such as a video camera is required to have an image stabilization function for preventing image blur due to a shake or the like, and various types of image stabilization methods are proposed. Among them, optical image stabilization, which has an image stabilization function by shifting a single lens or multiple lens units so as to have a component in a direction perpendicular to the optical axis, is widely used at present in a digital still camera, a video camera, and the like.
In addition, other than the above-mentioned image stabilization method, there are a method of rotating a part of an imaging lens about the center of curvature radius of the lens, and a method using a shiftable lens unit and a rotatable lens unit.
For instance, Japanese Patent Application Laid-Open No. H09-251127 discloses an optical system that rotates a part of an afocal unit or multiple lenses disposed on the most object side about the center of curvature radius for image stabilization. Japanese Patent Application Laid-Open No. 2003-202499 discloses an imaging lens including first to fourth lens units having positive, negative, positive and positive refractive powers, in which the second and third lens units are shiftable while the second, third, and fourth lens units are rotatable. The shiftable lenses and the rotatable lenses are moved for image stabilization.
However, the method of Japanese Patent Application Laid-Open No. H09-251127 has a problem in that optical performance is deteriorated when the image stabilization is performed because a rotation angle of the first lens unit is increased. In addition, the method of Japanese Patent Application Laid-Open No. 2003-202499 has a problem in that a light beam is vignetted so that a peripheral light amount ratio is decreased because the shift and the rotation are performed by two lens units in vicinity or in a rear side of an aperture stop.
In particular, when performing large image blur correction (hereinafter referred to as “large vibration isolation” in this specification) more than 50% of an angle of field at a telephoto end, an image blur correction amount is determined by a movement component in a direction perpendicular to the optical axis of a correction optical system. Therefore, because it is necessary to increase the movement component in the perpendicular direction for performing large vibration isolation, the deterioration of the optical performance and the decrease in peripheral light amount become conspicuous.
In addition, there is a method of rotating the lens unit itself so as to achieve both the optical performance and the peripheral light amount. However, a large actuator is necessary for driving the lens unit because the part to be moved has a large weight, which results in an increase of weight.